Technical Field
The present invention relates to a distribution device, distribution system, and distribution method.
Background Art
Monitoring technology whereby sensor device including sensors typified by an acceleration sensor, a displacement sensor, and the like is attached to a structure such as a building or bridge, thus monitoring the state of the structure, is known (NPL 1). The sensor device utilized in the monitoring technology executes a process of detecting change in the state of the structure (acceleration, displacement, and the like) in a constant cycle. The result of the process is temporarily recorded together with time information in the sensor device, or the like. Then, the recorded result is transmitted via, for example, a network or the like to an external device.
The sensor device executes a process for detecting a change in state in a constant cycle. Depending on the object or target of monitoring, the cycle may be an extremely short cycle. For example, in order to analyze vibration arising from microtremors or earthquakes, an acceleration sensor needs to continuously measure acceleration in a constant cycle of in the region of 5 to 10 milliseconds.
Meanwhile, in order to detect and record vibration and the like arising in a structure, the sensor device synchronizes time using time information provided from the exterior. This sensor device is connected on a network to an external device that manages time, and synchronize time using protocol known as NTP (Network Time Protocol) or RBS (Reference Broadcast Synchronization) (NPL 2 and 3). When using protocol like NTP, technology that corrects time information taking a transmission delay time into consideration is utilized (NPL 4).
PTL 1 discloses technology whereby multiple items of device having a radio clock reception function are such that the times of all the items of device are synchronized by acquiring a reference time using a standard time and frequency signal.
PTL 2 discloses technology whereby an amount of time correction is determined using the difference in time between a GPS-derived time and a stable, high accuracy atomic clock-derived time, and time synchronization of mutually connected base stations or communication devices is carried out via the Synchronous Ethernet (registered trademark).
PTL 3 discloses a time synchronization system wherein time synchronization is carried out using NPT when time synchronization requests transmitted from a client to a server reach a certain number.
PTL 4 discloses technology whereby an NTP server that has received a time synchronization request from an NTP client transmits determination information to the NPT client, and the client determines whether or not to carry out time synchronization using the determination information.